Images are formed in silver halide color photographic materials by reaction between oxidized silver halide developing agent, resulting from the imagewise reduction of silver halide to metallic silver, and a dye-forming compound known as a coupler. It has become common practice to modify photographic properties of the image, such as sharpness, granularity and contrast, by the use of a image modifying compound commonly referred to as a development inhibitor releasing (DIR) coupler. Such materials were first described in U.S. Pat. Nos. 3,148,062 and 3,227,554.
More recently, U.S. Pat. No. 4,248,962, 4,409,323, and 4,500,633 have described release compounds from which a development inhibitor is released from an intervening group, called a timing group, after that group is released from the carrier portion of the compound.
U.S. Pat. No. 4,248,962 describes release compounds represented by the structure COUP-TIME-PUG, where COUP is a coupler group, PUG is a photographically useful group and TIME is a timing group. The timing group can be represented by the structure: -Nu-LINK-E-where Nu is a nucleophilic group, LINK is a linking group that provide the appropriate spatial relationship to permit an intramolecular displacement reaction to occur and E is an electrophilic group.
The use of a timing group provides a way to separate the release function from the photographic function and permits these separate functions to be designed into the compound in an optimal manner. Thus, control over the rate, location and time of the release of the development inhibitor can be optimized by the use of a separate timing group.
In addition to development inhibitors other photographically useful groups may desirably be released in an imagewise manner during photographic processing. Such groups include development accelerators, complexing agents, toners, stabilizers, etc.
It has been difficult to provide heterocyclic nitrogen release compounds, such as pyrazolone couplers, that are substituted in the coupling position. Such compounds frequently are unstable, or have poor reactivity as couplers, or both. This is exacerbated when the substituent is an oxygen-linked group.
When it is desired that the photographically useful group released in the element not act in the immediate vicinity of the site of release, an intervening timing group preferably is used, as described in U.S. Pat. No. 4,248,962, referred to above. However, we have found that known timing groups are not ideal for attachment to pyrazolone couplers. With these couplers, there generally is a trade-off between the stability of the release compound and the ability of the timing group to rapidly release the photographically useful group.
Thus, a problem to be solved by this invention is to provide release compounds containing novel timing groups, especially those which can be attached to heterocyclic nitrogen carriers, such as pyrazolone couplers, to provide stable compounds that release photographically useful groups at a relatively rapid rate so as to provide a desired photographic effect.